---
title: "Biomass and the carbon neutral cycle"
subject: "Power Plant Design"
chapter: 1
key: "semester_8/power_plant_design:biomass-carbon-neutral-cycle"
source: https://www.bctengineer.com/q/semester_8/power_plant_design/biomass-carbon-neutral-cycle
site: BCT Engineering
---

# Biomass and the carbon neutral cycle

Power Plant Design · Chapter 1: Energy Sources and Electric Power Generation

- Asked in: 2079 Chaitra, 4 marks
- Video: [The Future of Energy: Carbon Neutral Biofuels - Explained in 7 Minutes](https://www.youtube.com/watch?v=xT1ZW72N55Y) — BioTech Whisperer
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_8/power_plant_design/biomass-carbon-neutral-cycle
- Whole chapter: https://www.bctengineer.com/md/semester_8/power_plant_design/chapter-1

## Question

Explain how bio-mass source of energy can maintain sustainable carbon neutral cycle?

## Short answer

Plants absorb CO₂ during growth; burning biomass releases the same CO₂ back. If regrowth matches harvest, the cycle is carbon neutral. Sustainable practices, efficient use, and minimal fossil inputs in processing are required to maintain the balance.

## Answer

A **carbon neutral cycle** means the CO₂ released when a fuel is used is equal to the CO₂ removed from the atmosphere to form that fuel, so the net change of atmospheric CO₂ is zero.

#### How biomass maintains it
1. **Absorption** – growing plants take CO₂ from air by photosynthesis and store the carbon in wood, leaves and crops.
2. **Use** – when biomass is burnt, gasified or digested (biogas), the stored carbon returns to the air as CO₂.
3. **Regrowth** – new plants grown on the same land absorb the same CO₂ again.

```text
     CO2 in atmosphere
      ^            |
      | burning    | photosynthesis
      |            v
  Energy use <-- Biomass (wood, crops,
  (heat,          residue, dung)
   power)
```
Fossil fuels, by contrast, release carbon that was locked underground for millions of years, so they add new CO₂ to the air.

#### Conditions for being truly carbon neutral
- Harvest must not exceed regrowth (sustainable forestry, replanting).
- Use residues and wastes that would decay anyway.
- Use efficient technologies (improved stoves, gasifiers, biogas) to get more energy per kg.
- Minimise fossil fuel used in harvesting, transport and processing.

If forests are cleared without replanting, the cycle breaks and biomass becomes a net CO₂ source.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. A carbon neutral cycle means
   A. CO2 released when used equals CO2 removed to form the fuel
   B. No CO2 is ever released
   C. CO2 is always increased
   D. Only oxygen is released
   Answer: A. Net change in atmospheric CO2 is zero. (Key point: Carbon neutral meaning)

2. Which order describes the cycle?
   A. Burn, grow, absorb
   B. Absorption by plants, release on use, regrowth absorbs again
   C. Release, release, release
   D. Regrowth only
   Answer: B. Plants absorb CO2, use returns it, and regrowth absorbs it again. (Key point: Three steps)

3. When does the cycle break?
   A. When harvest equals regrowth
   B. When residues are used
   C. When forests are cleared without replanting
   D. When efficient stoves are used
   Answer: C. Without replanting, biomass becomes a net CO2 source. (Key point: Conditions)

## Related in Power Plant Design

- [Biomass compared with geothermal energy](https://www.bctengineer.com/question.md?key=semester_8%2Fpower_plant_design%3Abioenergy-vs-geothermal) — Power Plant Design, chapter 1
- [Bio-energy with an example](https://www.bctengineer.com/question.md?key=semester_8%2Fpower_plant_design%3Abio-energy-example) — Power Plant Design, chapter 1
- [Why biomass is a renewable source](https://www.bctengineer.com/question.md?key=semester_8%2Fpower_plant_design%3Abiomass-renewable-claim) — Power Plant Design, chapter 1, asked 2×
- [Conventional, non-conventional sources and biomass](https://www.bctengineer.com/question.md?key=semester_8%2Fpower_plant_design%3Aenergy-sources-biomass) — Power Plant Design, chapter 1

## Related in other subjects

- [Synthetic fuel from biomass, bio fuel cells](https://www.bctengineer.com/question.md?key=semester_7%2Fenergy_environment_and_society%3Asynthetic-fuel-biofuel-cell) — Energy Environment and Society, chapter 3
- [Bio-chemical conversion of biomass](https://www.bctengineer.com/question.md?key=semester_7%2Fenergy_environment_and_society%3Abiochemical-conversion-biomass) — Energy Environment and Society, chapter 3
- [Role of electrical energy in sustainable development](https://www.bctengineer.com/question.md?key=semester_7%2Futilization_of_electrical_energy%3Aelectrical-energy-sustainable-development) — Utilization of Electrical Energy, chapter 1, asked 2×
- [First law for control mass; cycle; power and refrigeration](https://www.bctengineer.com/question.md?key=semester_2%2Ffundamental_of_thermodynamics_and_heat_transfer%3Afirst-law-control-mass-cycle) — Fundamental of Thermodynamics & Heat Transfer, chapter 4